Metallic glass composites with controllable work-hardening capacity

ABSTRACT

There are provided metallic glass matrix composites with controllable work-hardening capacity. In more detail, there are provided metallic glass matrix composite with controllable work-hardening capacity capable of having significantly excellent toughness due to a metastable second phase precipitated in-situ in a metallic glass matrix by polymorphic phase transformation during a solidification process without a separate synthetic process, and capable of controlling work-hardening capacity by measuring physical properties of a second phase and adjusting a volume fraction (V f ) of the second phase due to constant correlation between the physical properties (absorbed energy E t   a , a phase transformation temperature T Ms , or a hardness H 2nd ) of a metastable B2 second phase precipated in the metallic glass matrix and the absorbed energy (E p   a,V ) by work-hardening per unit volume fraction of the second phase in the metallic glass matrix.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0141240 filed in the Korean IntellectualProperty Office on Oct. 7, 2015, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to metallic glass composites withcontrollable work-hardening capacity.

(b) Description of the Related Art

In order to improve toughness of a structural material, research intomethods of introducing a second phase to prepare a composite has beenconducted with respect to various materials and processes. Particularly,in a case of metallic glass having high strength and elasticity buthaving brittleness, research into a technology of improving elongationby preparing a metallic glass matrix composite into which ceramic, acrystalline metal, or the like, is introduced as a second phase has beenvariously conducted. However, in the case of introducing ceramic as thesecond phase, there is a limitation in improving elongation of thecomposite, and in the case of introducing a ductile crystalline metal asthe second phase, there is a limitation in improving toughness of thecomposite due to a decrease in strength by post-yield work softening andan initial necking phenomenon.

A technology of improving mechanical properties with respective to ageneral crystalline alloy by preparing the composite as described abovehas been variously developed, but the technology has focused onimprovement of strength or processability, and it was known that inorder to improve toughness, alloy heat treatment, or improvement of asolidification method and an alloy design method is more effective thanpreparation of the composite. More specifically, a method of inserting ametal wire as a reinforcement material to significantly increaseelongation in order to improve mechanical properties of a crystallinemagnesium metal material has been disclosed in Korean Patent No.10-0513584, but in this method, toughness was not largely improved dueto a decrease in strength. In addition, a composite in which carbon andcarbide are introduced as second phases into a titanium alloy wasdisclosed in Korean Patent No. 10-0867290. In this case, the carbidereacted with various additives such as silicon (Si), chromium (Cr),titanium (Ti), vanadium (V), tantalum (Ta), molybdenum (Mo), zirconium(Zr), boron (B), calcium (Ca), and the like, to exist in a titaniumgrain boundary, such that strength was significantly improved, butelongation tended to be decreased, such that toughness was not largelyimproved. In addition, a technology for a titanium/aluminum composite inwhich a ceramic reinforcement material is inserted has been disclosed inKorean Patent Nos. 10-0564260 and 10-1197581, but there were limitationsin that an effect of improving strength was excellent, but toughness wasnot improved.

However, since in the case of metallic glass, although there is atendency to occur brittle fracture, unlike the crystalline alloy, it isdifficult to control mechanical properties of the metallic glass by heattreatment, the solidification method, and the alloy design method, atechnology for improving mechanical properties, particularly, toughness,by preparing a composite has been more actively developed. A technologycapable of having a composite structure formed by partialcrystallization in a metallic glass in the case in which Fe basedmetallic glass contains one element selected from Cu, Co, Al, Ti, and Zrin a range of 1 to 5% to thereby apply a strip casting process, whichmay not be applied due to brittleness of metallic glass, has beendisclosed in Korean Patent No. 10-0723162. However, in the Related ArtDocument, there was a limitation in that a quantitative value forimproving mechanical properties of an alloy except for processabilityimprovement was not disclosed. A technology of improving toughness bypreparing a composite containing metallic glass and crystalline copperparticles as a second phase using a powder sintering method has beendisclosed in Korean Patent No. 10-0448152. However, as post-yieldstrength is decreased, it is impossible to implement high toughness.Therefore, in order to implement ultra-high toughness in the metallicglass, a method capable of implementing work-hardening capacity ofincreasing post-yield strength by designing a new composite structureand systemically controlling the work-hardening capacity has beenrequired.

Recently, it was reported that as a material capable of being introducedinto the metallic glass to implement work-hardening capacity andimproving toughness, a CuZr B2 crystalline phase transformation alloy issuitable, but a specific technology for a work-hardening device and amethod of improving toughness has not yet been developed. A phasetransformation alloy (shape memory alloy or super-elastic alloy) is amaterial capable of significantly improving toughness throughmartensitic transformation under specific temperature and stressconditions. The reason is that the phase transformation alloy causes alarge strain hardening section after phase transformation by partiallyconsuming energy applied from the outside at the time of phasetransformation as phase transformation energy and preventing stressconcentration through a plurality of shear bands formed by interactionswith a metallic glass matrix, thereby having a deformation behaviorsimilar to a work-hardening behavior of a crystalline material.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention provides a metallicglass matrix composite capable of systemically controllingwork-hardening capacity thereof by controlling physical properties of asecond phase and adjusting a volume fraction of a phase, whileimplementing post-yield work-hardening by allowing a metastable secondphase of which phase tranformation from an austenite B2 phase to amartensite phase may occur to be precipitated in-situ in a metallicglass matrix by polymorphic phase transformation during a solidificationprocess without a separate synthetic process.

An exemplary embodiment of the present invention provides a metallicglass matrix composite capable of adjusting a volume fraction of asecond phase in the composite through casting process control due tofixed correlation between physical properties (absorbed energy, a phasetransformation temperature, and hardness) of a precipitated second phaseand absorbed energy per unit volume fraction of the second phase tocontrol work-hardening caapcity.

Another embodiment of the present invention provides a metallic glassmatrix composite capable of preventing brittle fracture of a metallicglass alloy matrix by decreasing concentration of stress applied to amaterial during a deformation process through phase transformation of ametastable second phase precipitated in the metallic glass matrix bypolymorphic phase transformation during a solidification without aseparate synthetic process into a stable phase, and capable of having alarge strain hardening section after phase transformation to improvetoughness through a work-hardening behavior.

In the metallic glass matrix composite according to the exemplaryembodiment of the present invention, a crystalline metastable secondphase formed through polymorphic phase transformation may beprecipitated, such that work-hardening for improving toughness ofmetallic galss through phase transformation of the metastable secondphase occuring at the time of deformation may be performed.

In addition, the metallic glass matrix composite according to theexemplary embodiment of the present invention may be a metallic glassmatrix composite capable of systemically adjusting a precipitatedphase-transformable metastable second phase to control work-hardeningcapacity, and may contain about 35 to 58 at % of Ti, about 35 to 50 at %of Cu, about 4.5 to 12 at % of Ni, and about 0.5 to 5 at % of Si, andfurther contain one or more elements selected from Zr, Hf, V, Nb, Ta,Nb, and Cr, which are early transition metals (ETM), and Al and Sn,which are post transition metals (PTM), in a range of about 1 to 15 at%.

In detail, the second phase formed by polymorphic phase transformationduring the solidification may have a composition similar to that of thematrix as a metastable phase generally formed in a rapid coolingprocess, and has a tendency to be phase-transformed into a stable phase.Particularly, due to the tendency as described above, the crystallinemetastable phase may serve as a phase transformation media of which aphase is transformed at the time of deformation of the material, andphase transformation of the crystalline metastable phase may serve as amechanism relaxing stress applied to the material to inhibitconcentration of the stress, thereby preventing brittle fracture of themetallic glass matrix.

The metallic glass matrix composite according to the exemplaryembodiment of the present invention may be an alloy containing about 35to 58 at % of Ti, about 35 to 50 at % of Cu, about 4.5 to 12 at % of Ni,and about 0.5 to 5 at % of Si so as to enable formation of themetastable second phase by polymorphic phase trasnformation whileenabling metalligc glass formation of a matrix metal by improvingliquid-phase stability.

Further, one or more elements selected from Zr, Hf, V, Nb, Ta, Nb, andCr, which are early transition metals (ETM), and Al and Sn, which arepost transition metals (PTM) may be added to the metallic glass matrixcomposite in a range of about 1 to 15 at %.

Here, since Zr, Hf, V, Nb, Ta, Nb, and Cr, which are the earlytransition metals (ETM), and Al and Sn, which are the post transitionmetals (PTM) are elements improving glass forming ability at the time ofbeing added to a quaternary alloy, a larger metallic glass matrixcomposite may be prepared by adding these elements, and characteristicsof the metastable second phase precipitated by polymorphic phasetransformation may be adjusted through multiple elements. However, inthe case in which a content of the additionally added element is about15 at % or more, another phase in addition to a phase-transformable B2phase may be additionally multi-precipitated, which is not preferable.

Further, in the metallic glass matrix composite according to theexemplary embodiment of the present invention, since corelation betweeneach of the properties of the phase-transformable metatable second phaseand work-hardening capacity of the composite is fixed, work-hardeningcapacity of the composite may be controlled by finally measuring thephysical properties (absorbed energy E^(t) _(a), a phase transformationtemperature h_(Ms), or a hardness H_(2nd)) of the second phase in themetallic glass matrix to calculate absorbed energy by work-hardening perunit volume fraction of the second phase, and adjusting the volumefractrion of the second phase in the composite through casting processcontrol.

In detail, the absorbed energy (J/cm³·vol %) by work-hardening per unitvolume fraction of the phase-transformable metastable second phase(J/cm³·vol %) may be calculated usign the following Equation, and aneffect caused by the volume fraction of the second phase may beexcluded.

$E_{a,V}^{p} = {\left( {{\int_{\varepsilon_{y}}^{\varepsilon_{f}}{\left( {\sigma - \sigma_{y}} \right){\varepsilon}}} - \frac{\left( {\sigma_{f} - \sigma_{y}} \right)^{2}}{2}} \right)/V_{f}}$

(ε_(y): yield strain, ε_(f): fracture strain, σ_(y): yield stress,σ_(f): fracture stress, and Vf: volume fraction of second phase inmetallic glass matrix composite)

Absorbed energy by plastic deformation is a value correspodning totoughness at the time of performing a tensition test, work-hardeningability may be quantitatively compared by reflecting work-hardeningrate, an increase in elongation, an increase in strength, and adifference in elastic modulus between materials. Further, CorrelationEquations between the physical properties (E^(t) _(a), T_(Ms), orH_(2nd)) of the phase-transformable metastable second phase and E^(p)_(a,V) may be E^(p) _(a,V)=A₀E^(t) _(a)−B₀ (A₀=5(±0.5)/10³,B₀=6(±3)/10²), E^(p) _(a,V)=C₀T_(Ms)−D₀ (C₀=2.6(±0.2)/10³,D₀=1.6(±0.2)/10), and E^(p) _(a,V)=E₀H_(2nd)+F₀ (E₀=−5(±0.5)/10³,F₀=2.7(±0.5)), (unit: E^(p) _(a,V)(J/cm³vol %), H_(2nd)(HV), T_(MS)(K),E¹ _(a)(J/cm³), respectively, these Correlation Equations may be fixedin the metastable second phase precipitated in a composition regionaccording to the exemplary embodiment of the present invention.Therefore, in the case of measuring the physical properties (E^(t) _(a),T_(Ms), or H_(2nd)) of the phase-transformable metastable second phaseaccording to the exemplary embodiment of the present invention, theabsorbed energy by work-hardening per unit volume fracture of the seocndphase may be quantitatively calucuated through these CorrelationEquations. In addition, according to the exemplary embodiment of thepresent invention, in an alloy system in a boundary composition regionin which a crystalline metastable phase and bulk metallic glass may beformed, the volume fraction of the phase-transformable second phase maybe adjusted by adjusting a suction casting process condition.

The process conditions controlled according to the exemplary embodimentof the present invention may be three, that is, an output power of arcplasma, a gas pressure when a molten metal is injected into a mold, anda cooling capacity through the mold. More specifically, the output powerof the arc plasma may be determined by adjusting an output voltage andan output current, and the higher the output power, the higher thevolume fraction of the second phase. In addition, the higher the gaspressure, the lower the volume fraction of the seocnd phase. Further,the cooling capacity may be changed depending on a diameter and a shapeof the mold, water cooling, or the like, and the thickner the testsample prepared in the mold, the lower the cooling capacity and thehigher the volume fraction of the second phase. Therefore, the metallicglass matrix composite with controllable work-hardening capacity may beprepared by adjusting the deduced E^(q) _(a,V) value and the volumefraction of through the casting process control.

According to an embodiment of the present invention, the metallic glassmatrix composite having a structure in which the metastable second phaseis precipitated in the metallic glass matrix by polymorphic phasetransformation may be provided without a separate additional process.

Further, the metallic glass matrix composite according to the presentinvention may prevent brittle fracture of the metallic glass matrix bystress relaxation and large strain hardening behavior accompanied whenthe metastable second phase precipiated by polymorphic phasetransformation is transforemd into the stable phase, thereby making itpossible to significantly improve toughness.

A prepartion method of the metallic glass matrix composite according tothe present invention, which is a method capable of starting from amother element metal, which is a raw material, to complete the alloyingand production of the composite in a single process, may significantlydecrease a cost and production time as compared to a multi-stepcomposite preparation method using the existing metal power, which iscomplicated and requires a large cost.

Particularly, in the metallic glass matrix composite according to theexemplary embodiment of the present invention, Correlation Equationbetween the physical properties of the phase-transformable metastablesecond phase and work-hardening capacity of the composite may be fixed,such that the work-hardening of the metallic glass matrix composite maybe easily controlled, and the related Equations may be utilized as amethod for predicting and evaluating work-hardening capacity of thecomposite. More specifically, since Equations suggested according to theexemplary embodiment of the present invention includes only the absorbedenergy E^(t) _(a), the phase transformation temperature T_(Ms), or thehardness H_(2nd) as variables, these Equations may be utilized in mainEquations and evaluation methods in computer simulations, and the like,for effectively controlling work-hardening capacity of the composite bycontrolling physical properties of the second phase. In addition,work-hardening capacity of the composite may be easily controlled byeffectively adjusting the volume fraction fo the phase-transformablemetastable second phase in the metallic glass mnaterix in the alloysystem in the boundary composition region in which the crstallinemetastable phase and the bulk metallic glass may be formed. Therfore,work-hardening capacity of the composite may be predicted only bymeasuring the physical properties (E^(t) _(a), T_(Ms), or H_(2nd)) ofthe second phase of the prepared composite, and it is possible toprepare a metallic glass matrix composite with controllablework-hardening capacity, so as to have physical properties to be desiredby using Correlation Equations between the physical properties of thephase-transformable metastable second phase and an increase inwork-hardening capacity of the metallic glasss matrix composite andcasting process control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pseudo-binary phase diagram of a Ti—Cu—Ni ternary alloy.

FIG. 2 is a differential scanning calorimetry result illustrating aneffect of adding Si to the Ti—Cu—Ni alloy.

FIG. 3 is a scanning electron microscope (SEM) photograph of a testsample prepared according to an exemplary embodiment of the presentinvention and a graph illustrating X-ray diffraction analysis resultthereof.

FIG. 4 is a result obtained by observing cross-sectional micro-structureof metallic glass matrix composites having various volume fractions of asecond phase, prepared by adjusting an arc plasma current in aTi₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂ alloy composition according to an exemplaryembodiment of the present invention using an optical microscope.

FIG. 5 illustrates a stress-strain diagram obtained by performing auniaxial compression test on the metallic glass matrix composites havingvarious volume fractions of the second phase, illustrated in FIG. 4.

FIG. 6 is a high-energy X-ray diffraction analysis result illustrating areal-time phase transformation behavior at the time of compressing atest sample prepared using an alloy composite according to an exemplaryembodiment of the present invention.

FIG. 7 illustrates a stress-strain diagram obtained by performing acompression test on phase-transformable metastable crystalline alloys,Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ (x=3, 6, and 8 at %) according to anexemplary embodiment of the present invention.

FIG. 8 is a graph illustrating a corrrelation between a volume fractionof a second phase of a metallic glass matrix composite prepared byprocess control in Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions(x=3, 6, and 8 at %) according to an exemplary embodiment of the presentinvention and a change in absorbed energy (E^(p) _(a)) bywork-hardening.

FIG. 9 is a graph illustrating a correlation between absorbed energy(E^(t) _(a)) of metastable crystalline alloys inTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloy compositions (x=1,2,3,4,5,6,7,8,and 9 at %) according to the exemplary embodiment of the presentinvention, and absorbed energy (E^(p) _(a,V)) by work-hardening per unitvolume fraction of a second phase formed in a metallic glass matrixcomposite prepared using each of the cmpositions.

FIG. 10 is a graph illustrating a correlation between a martensite-starttemperature (T_(Ms)) of a phase-transformable metastable second phase incomposites prepared using Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloycompositions (x=3, 6, and 8 at %) and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloycompositions (x=1,2,3,4,5,6,7,8, and 9 at %) according to the exemplaryembodiment of the present invention and absorbed energy (E^(p) _(a,V))by work-hardening per unit volume fraction of the second phase.

FIG. 11 a graph illustrating a correlation between a hardness (H_(2nd))of the second phase in the composites prepared using theTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and the Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloy compositions(x=1,2,3,4,5,6,7,8, and 9 at %) according to the exemplary embodiment ofthe present invention and the martensite-start temperature (T_(Ms)).

FIG. 12 is a graph illustrating a correlation between absorbed energy(E^(p) _(a,V)) by work-hardending per unit volume fraction of the secondphase in the metallic glass matrix composite preapred usingTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloy compositions (x=1,2,3,4,5,6,7,8,and 9 at %) according to the exemplary embodiment of the presentinvention and the hardness (H_(2nd)) of the second phase.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings andTables.

A metallic glass matrix composite according to the present exemplaryembodiment is composed of a Ti—Cu—Ni—Si based metallic glass matrix anda metastable second phase precipated by polymorphic phasetransformation.

The second phase formed by polymorphic phase transformation during asolidification process, which is a metastable phase having a compositionsimilar to a matrix composition, tends to be changed to a stable phaseby an external temperature or stress. Due to characteristics of themetatable phase, the metastable phase serves as a phase transformationmedia at the time of deformation of a material, phase transformation ofa crystalline metastable phase as described above serves as a mechanismof relaxing stress applied to the material, thereby preventing brittlefracture of the metallic glass matrix.

Therefore, the present inventors developed a metallic glass compositehaving excellent strength and toughness due to work-hardeningcharacteristics obtained by precipitating a phase-transformablecrystalline metastable second phase by stress in a high-strength Tibased metallic glass matrix through polymorphic phase transformation ofa matrix metal caused by metal solidification.

To this end, glass forming ability (GFA) should be high, a metastablesecond phase should be precipitaed through polymorphic phasetransformation of a matrix metal at the time of solidification, andphase transformation of the precipitated second phase to a stable phaseshould easily occur.

Ti is a main element of a Ti based metallic glass material havingexcellent mechanical properties, and has high liquid-phase stability asa deep eutectic composition in the case of being alloyed with Cu and Ni,thereby having excellent glass forming ability. In addition, a TiCu(Ni)metastable phase, which is a main phase according to an exemplaryembodiment of the present invention, tends to be precipitated as ametastable phase through polymorphic phase transformation durignsolidification.

In consideration of the facts as described above, a ternary eutecticcomposition represented by Composition Formula, Ti₅₀Cu₄₂Ni₈ may bedetermined as a base composition by evaluating glass forming ability invarious compositions with respect to ternary alloys composed of Ti, Cu,and Ni. In an alloy system composed of Ti, Ni, and Cu, a size differencebetween Ti (0.147 nm), which is a main element, and Cu(0.128 nm), and asize difference between Ti and Ni(0.124 nm) were about 13% and about16%, respectively, there are large differences in atom size, and heat ofmixing of Ti—Cu and Ti—Ni are about −67 kJ/mol·atom and about −140kJ/mol·atoms, respectively, which are large negative values, such thatthe alloy system is consistent with heuristics, and the Ti₅₀Cu₄₂Ni₈composition, which is a composition similar to an eutectic composition,has excellent glass forming ability due to excellent liquid-phasestability. Therefore, even though the Ti₅₀Cu₄₂Ni₈ composition is aternary alloy, the Ti₅₀Cu₄₂Ni₈ composition has excellent glass formingability, and as a result, the Ti₅₀Cu₄₂Ni₈ composition has a bulkmetallic glass formation maximum diamter of about 2 mm.

FIG. 1 is a pseudo-binary phase diagram of a Ti—Cu—Ni ternary alloy. Asdescribed above, a Ti₅₀Cu₄₂Ni₈ alloy composition, which is a compositionforming a ternary eutectic reaction, is an alloy composition havingexcellent glass forming ability based on excellent liquid-phasestablity.

FIG. 2 is a differential scanning calorimetry result illustrating aneffect of adding Si to the Ti—Cu—Ni alloy. Glass forming ability isexcellent in a Ti₅₀Cu₄₂Ni₈ ternary alloy composition region, but it isimpossible to precipiate a single metastable second phase by polymorphicphase transformation through polymorphic precipitation during asolidification process. However, as illustrated in FIG. 2, it may beconfirmed that as a small amount of Si is added to the alloy compositionregion, a stable region of a phase-transformable metastable B2 phase isexpanded, such that the B2 phase may be precipitated alone bypolymorphic phase transformation during solidification.

Therefore, the present inventors developed an alloy composition whichhas excellent glass forming ability and in which a metal stable B2second phase may be precipiated by polymorphic phase transformation byadding Si at a content of about 0.5 at % or more based on theTi₅₀Cu₄₂Ni₈ alloy composition. Here, in the case in which the content ofadded Si is more than 5 at %, glass forming ability is rapidlydeteriorated, such that it become difficult to prepare a composite evenby adjusting a cooling rate. Results obtained by confirming glassforming ability and precipiated second phase of various alloycompositions according to an exemplary embodiment of the presentinvention are illustrated in the following Table 1.

TABLE 1 Ti—Cu—Ni—X Test Sample System Composition 2 mm 3 mm 5 mmCrystalline phase (C) TiCuNi Ti₄₂Cu₅₀Ni₈ C multi-phases Ti₄₆Cu₄₆Ni₈ Cmulti-phases Ti₄₈Cu₄₂Ni₁₀ C multi-phases Ti₅₀Cu₄₀Ni₁₀ a + C multi-phasesTi₅₀Cu₄₂Ni₈ A + C  multi-phases Ti₅₀Cu₄₄Ni₆ a + C multi-phasesTi₅₅Cu₃₇Ni₈ C multi-phases Ti₆₂Cu₃₀Ni₈ C multi-phases TiCuNiZrTi₄₅Cu₄₃Ni₇Zr₅ A  a + C multi-phases Ti₄₄Cu₄₂Ni₇Zr₇ A  a + Cmulti-phases Ti₄₃Cu₄₁Ni₇Zr₉ A A + c multi-phases TiCuNiSiTi_(49.5)Cu₄₂Ni₈Si_(0.5) a + C single B2 Ti₄₉Cu₄₂Ni₈Si₁ A + c  single B2Ti₄₈Cu₄₁Ni₈Si₃ A + c  single B2 Ti₄₇Cu₄₁Ni₇Si₅ a + C single B2Ti₄₈Cu₄₀Ni₅Si₇ C multi-phase Ti₄₈Cu₄₅Ni₂Si₅ C multi-phase TiCuNiSiSnTi₅₂Cu₃₈Ni₇Si₁Sn₂ a + C single B2 Ti₅₁Cu₃₉Ni₇Si₁Sn₂ a + C single B2Ti₅₀Cu₄₀Ni₇Si₁Sn₂ a + C single B2 Ti₄₉Cu₄₁Ni₇Si₁Sn₂ a + C single B2Ti₄₈Cu₄₂Ni₇Si₁Sn₂ a + C single B2 Ti₄₇Cu₄₃Ni₇Si₁Sn₂ a + C single B2Ti₄₆Cu₄₄Ni₇Si₁Sn₂ a + C single B2 Ti₄₅Cu₄₅Ni₇Si₁Sn₂ a + C single B2Ti₄₄Cu₄₆Ni₇Si₁Sn₂ a + C single B2 TiCuNiSiSn(Al)Zr Ti₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂A A + c single B2 Ti₄₅Cu₄₃Ni₇Si₁Sn₂Zr₂ A  a + c single B2Ti₄₃Cu₄₅Ni₇Si₁Sn₂Zr₂ A A + c single B2 Ti₄₂Cu₄₃Ni₇Si₁Sn₂Zr₅ A A + csingle B2 Ti₄₁Cu₄₄Ni₇Si₁Sn₁Al₁Zr₅ A A + c single B2 Ti₄₀Cu₄₅Ni₇Si₁Sn₂Zr₅A A a + C single B2 Ti₄₅Cu₃₈Ni₇Si₁Sn₂Zr₇ A A + c single B2Ti₄₄Cu₃₉Ni₇Si₁Sn₁Al₁Zr₇ A A + c single B2 Ti₄₃Cu₄₀Ni₇Si₁Sn₂Zr₇ A A + csingle B2 Ti₄₂Cu₄₁Ni₇Si₁Sn₁Al₁Zr₇ A A a + C single B2Ti₄₂Cu₄₁Ni₇Si₁Sn₂Zr₇ A A a + C single B2 Ti₃₉Cu₃₈Ni₇Si₄Sn₅Zr₇ a + Cmulti-phase TiCuNiSiSnZr(Cr, Ti₄₄Cu₃₇Ni₇Si₁Sn₂Zr₇Cr₂ A + c  single B2 V,Hf, Ta, Nb) Ti₄₄Cu₃₇Ni₇Si₁Sn₂Zr₇V₂ A + c  single B2Ti₄₄Cu₃₇Ni₇Si₁Sn₂Zr₇Hf₂ A A + c single B2 Ti₄₄Cu₃₇Ni₇Si₁Sn₂Zr₇Ta₂ A A +c single B2 Ti₄₃Cu₃₈Ni₇Si₁Sn₂Zr₇Nb₂ A A A + c  single B2Ti₄₂Cu₃₇Ni₇Si₁Sn₂Zr₇Nb₄ A A + c A + c  single B2 Ti₄₀Cu₃₅Ni₇Si₁Sn₂Zr₉Nb₆a + C multi-phase Ti₃₉Cu₃₄Ni₇Si₁Sn₂Zr₉Nb₈ C multi-phase

In Table 1, A and a indicate a metallic glass phase, wherein A indicatesa metallic glass phase of which a volume fraction is large and aindicates a metallic glass phase of which a volume fraction is small,and C and c indicate cystalline phase, wherein C indicates a crystalinephase of which a volume fraction is large and c indicates a crystallinephase of which a volume fraction is small. As illustrated in Table 1, itmay be appreciated that in the cases of test sample in which additionelements are added based on a TiCuANi based alloy, a composite in whichthe metallic glass phase and the crystalline phase are mixed is formedin the vicinity of a maxium size at which the metallic glass phase maybe formed. Particularly, it may be confirmed that in the case of addingSi in a range of about 0.5 to 5 at %, a single metastable B2 phase isprecipitated, and in the case in which one or more elements selectedfrom Zr, Hf, V, Nb, Ta, and Cr, which are early transition metals (ETM),and Al and Si, which are post transition metals (PTM) is additionallyadded in a range of about 1 to 15 at %, the single metastable B2 phasemay also be precipitated in the metallic glass matrix throughpolymorphic phase transformation. However, in the case in which acontent of the additionally added element is about 15 at % or more,another phase may be polymorphically precipitated in addition to the B2phase by phase transformation, which is not preferable.

Features of a metallic galss matrix composite in which crystallinemetastable second phase is precipitated through polymorphic phasetransformation during the solidification process in Ti—Cu—Ni—Si basedalloy prepared by rapid solidification within the above-mentionedcomposition range were analyzed as follows.

FIG. 3 is a scanning electron microscope (SEM) photograph of a testsample prepared according to an exemplary embodiment of the presentinvention and a graph illustrating X-ray diffraction analysis resultthereof. The test sample has a Ti₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂ composition, and itmay be confirmed that the test the test sampe is composed of a matrixportion having a light color and a precipiation portion having a darkcolor in the SEM photograph. It may be appreciated from the accompanyingX-ray diffraction alalysis result that the matrix portion is a metallicglass phase, and the precipitation portion, which is a crystallinephase, is a metastable B2 second phase formed through polymorphic phasetransformation during the solidification process.

FIG. 4 is an optical microscope photograph illustrating cross sectionsof metallic glass matrix composites having various volume fractions of asecond phase, prepared using a Ti₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂ composition amongalloys according to an exemplary embodiment of the present invention. Inthe case of preparing a metallic glass matrix composite by porcesscontrol with respect to the same composition, a metastable B2 secondphase of which absorbed energy (E^(t) _(a)) and T_(Ms) were the same aseach other was precipitated. In detail, in the case of adjusting anintensity of an output current to about 50, 100, 150, 200, and 250 Aunder the condition that an output voltage of an arc plasma meltingdevice is about 30 V, composite having metastable B2 second phase (darkregion) having volume fractions of about 5.5 Vol %, about 12.3 Vol %,about 51.2 Vol %, about 80.1 Vol %, and about 84 Vol % in theTi₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂ composition, respectively, and metallic glassmatrix (bright region) having the residual volume fractions,respectively, were prepared. The reason may be that a meltingtemperature and flowability of a molten metal are changed depending onthe output power (output voltage: about 5 to 50 V, output current; about30 to 300 A), and thus, a supercooling degree at the time ofsolidification is changed, which affects formation of the metasatble B2second phase formed by allotropic transformation in the metallic glassmatrix. Here, in the case in which the output power is excessively low(the output voltage is less than about 5 V or the output current is lessthan about 30 A), it may be difficult to completely melt a material, andin the case in which output power is excessively high (the outputvoltage is more than about 50 V or the output current is more than about300 A), a change in composition may occur due to vaporization of aconsitution element in the material. Further, in the case in which aninjection pressure of the molten metal into a copper mold at the time ofcasting is adjusted (about 0 to 600 torr), there is a difference incooling capacity due to a change in flowabilioty in the mold, such thatit is possible to control the volume fraction of the second phasedependin on the difference in crystallinity. In the case in which thecasting is performed at a low pressure of about 10 torr based on acurrent amount of about 100 A, it is possible to obtain a second phasewith a high volume fraction of about 90 vol %, and in the case in whichthe casting is performed at a high pressure of about 400 torr, it ispossible to a second phase with a low volume fraction of about 10 vol %.Here, in the case in which the injection pressure is excessively high(more than about 600 torr), air bubbles are injected due to a turbulencephenomenon in the molten metal, voids may be excesively formed in thetest sample, which Is not preferable in view of preparing a suitabletest sample. In addition, a cooling rate condition having a largeinfluence on glass forming ability of the alloy may also have asignficant influence on controlling the volume fraction of thecomposite, and in the case of the alloy composition according to thepresetn invention, it is preferable to perform the casting whileadjusting cooling capacity in a range of about 10¹-10⁴ K/s inconsideration of glass forming ability.

FIG. 5 illustrates a stress-strain diagram obtained by performing auniaxial compression test on the metallic glass matrix compositesillustrated in FIG. 4. In the case in which a volume fraction of aphase-transformable metastable B2 second phase is low (about 5.5 vol %),the metallic glass matrix composite has mechanical properties similar tothose of metallic glass having brittleness, there is almost nowork-hardening capacity, but as the volume fraction of the second phase,the work-hardening capacity of the composite is increased with aconstant tendency. Therefore, it may be appreciated that in the case ofadjusting a suction casting process condition to control the volumefaction of the second phase while confirming contribution to a change inabsorbed energy by work-hardening per unit volume fraction of therelated second phase, it is possible to control work-hardening capacityof the metallic glass matrix composite.

FIG. 6 is a high-energy X-ray diffraction analysis result illustrating areal-time phase transformation behavior at the time of compressing acomposite test sample prepared using the Ti₄₈Cu₄₀Ni₇Si₁Sn₂Zr₂ alloycomposition. Generally, in the case of structure analysis usinghigh-energy X-ray, it is easy to observe phase transformation in a bulktype test sample due to high permeability, and a phase transformationbehavior of about 3 mm bulk test sample prepared according to thepresent exemplary embodiment at the time of compression was real-timeanalyzed usig the characteristics as described above. As an analysisresult, it may be clearly confirmed that in the second phase existing asthe B2 phase before applying stress thereto, phase transformation to amartensite phase occurred under a compression stress of about 1900 MPa(in the vicinity of a yield point of the material). This is clearlyobserved in both a vertical direction (left) and a horizontal direction(right) of the high-energy X-ray beam.

FIG. 7 illustrates a stress-strain diagram obtained by performing acompression test on phase-transformable metastable B2 crystallinealloys, Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ (x=3, 6, and 8 at %). Asillustraed in FIG. 7, it may be appreciated that in the case ofadjusting contents of Ti and Ca, absorbed eneryg may be controlled fromA=about 131.3 J/cm³ to B=about 78.0 J/cm³ and C=about 27.5 J/cm³, andyield stress (first yield by stress induced phase transformation) wasalso significantly decreased as illustrated in FIG. 7. The difference asdescribed above is caused by a differnce in properties of the formedmetastable B2 phase, which may be confirmed from the fact thatmartensite-star temperatures (T_(Ms)) were different from each other(A=about 189 K, B=about 77 K, and C=about −28 K (estimated values byfitting result values)).

FIG. 8 is a graph illustrating a corrrelation between a change inabsorbed energy (E^(p) _(a)) by work-hardening and a volume fraction ofa second phase of metallic glass matrix composites prepared by processcontrol in Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6,and 8 at %). In detail, absorbed energy obtained by deformation(work-hardening) after first yielding of the metallic glass matrixcomposite containg the phase-transformable metastable B2 phase iscalculated using Equation

$E_{a,V}^{p} = {\left( {{\int_{\varepsilon_{y}}^{\varepsilon_{f}}{\left( {\sigma - \sigma_{y}} \right){\varepsilon}}} - \frac{\left( {\sigma_{f} - \sigma_{y}} \right)^{2}}{2}} \right)/V_{f}}$

(ε_(y): yield strain, ε_(f): fracture strain, σ_(y): yield stress,σ_(f): fracture stress, M: elastic modulus), and a change in absorbedenergy by work-hardening depending on the volume fraction of the secondphase in each of the composition is illustrated in FIG. 8. Asillustrated in FIG. 8, as the volume fraction (V_(f)) of thephase-transformable metastable B2 second phase is increased, or themartensite-start temperature (T_(Ms)) of the second phase is increased,the absorbed energy by work-hardening is relativley increased, and as agradient of a linear fitting function of data obtained using Equation isincreased, the volume of the phase-transformable second phase isincreased, and thus, a work-hardening capacity increase rate of thecomposite prepared using the corresponding composition is increased.

FIG. 9 is a graph illustrating a correlation between absorbed energy(E^(t) _(a)) of metastable B2 crystalline alloys inTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloy compositions (x=1,2,3,4,5,6,7,8,and 9 at %), and absorbed energy (E^(p) _(a,V)) by work-hardening perunit volume fraction of a second phase formed in a metallic glass matrixcomposite prepared using each of the cmpositions. Here, the absorobedenergy of the phase-transformable B2 second phase is obtained byintegrating the stress-strain diagram obtained by performing acompression test on an alloy prepared as a single B2 cystalline phase.According to FIG. 9, as the absorobed energy of the phase-transformableB2 second phase is increased, absorbed energy of the compositecontaining a second phase thereof by work-hardening is increased, andthus, plastic deformability is large. Correlation Equation therebetweenis as follows: E^(p) _(a,V)=A₀E^(t) _(a)−B₀(A₀=5±0.5/10³,B₀=6±3/10²).Work-hardening capacity of the composite may be controlled by measuringthe absorbed energy (E^(t) _(a)), which is one of the physicalproperties, of the phase-transformable metastable B2 second phaseprecipated in the composite to calculate absorbed energy (E^(p) _(a,V))by work-hardening per unit volume fraction of the second phase formed inthe metallic glass matrix composite prepared using each of thecompositions.

FIG. 10 is a graph illustrating a correlation between a martensite-starttemperature (T_(Ms)) of a phase-transformable metastable second phase incomposites prepared using Ti_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloycompositions (x=3, 6, and 8 at %) and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloycompositions (x=1,2,3,4,5,6,7,8, and 9 at %) and absorbed energy (E^(p)_(a,V)) by work-hardening per unit volume fraction of the second phase.In the case of the composition according to the exemplary embodiment,since the martensite-start temperature was in a measurement temperaturerange of a generally used measurement apparatus, a phase transformationtemperature value was estimated by extrapolation using CorrelationEquation between the absorbed energy of the metastable B2 second phaseand the martensite-start temperature, and in order to distinguish theestimated value from a measured value, the estimated value was indicatedby a circle in FIG. 10. According to FIG. 10, as the martensite-starttemperature is increased, the absorbed energy of the composite bywork-hardening is increased. Therefore, plastic deformability isincreased, and Correlation Equation therebetween is as follows: E^(p)_(a,V)=C₀T_(Ms)−D₀(C₀=about 2.6±0.2/10³, D₀=about 1.6±0.2/10).Work-hardening capacity of the composite may be controlled by measuringthe martensite-start temperature (T_(Ms)), which is one of the physicalproperties, of the phase-transformable metastable B2 second phaseprecipitaed in the composite to calculate the absorbed energy (E^(p)_(a,V)) by work-hardening per unit volume fraction of the second phaseformed in the metallic glass matrix composite prepared using each of thecompositions.

FIG. 11 a graph illustrating a correlation between a hardness (H_(2nd))of the second phase in the composites prepared using theTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and the Ti_(53-x)Cu_(37+x)N₇Si₁Sn₂ alloy compositions(x=1,2,3,4,5,6,7,8, and 9 at %) and the martensite-start temperature(T_(Ms)). According to FIG. 11, T_(Ms) of the phase-transformablemetastable B2 second phase may be replaced with and represented by thehardness, which is one of the physical properties, of the second phasein the composite using Correlation Equation between T_(Ms) and H_(2nd),in other words, H_(2nd)=about 469.6±10−0.33±0.1.

FIG. 12 is a graph illustrating a correlation between absorbed energy(E^(p) _(a,V)) by work-hardending per unit volume fraction of the secondphase in the metallic glass matrix composite preapred usingTi_(51-x)Cu_(37+x)Ni₇Si₁Sn₂Zr₂ alloy compositions (x=3, 6, and 8 at %)and Ti_(53-x)Cu_(37+x)Ni₇Si₁Sn₂ alloy compositions (x=1,2,3,4,5,6,7,8,and 9 at %) and the hardness (H_(2nd)) of the second phase. According toFIG. 12, as a hardness value of the phase-transformable metastable B2second phase is decreased, the absorbed energy of the compositecontaining the B2 phase as a second phase by work-hardening isincreased, and thus plastic deformability is increased. CorrelationEquation therebetween is as follows: E^(p) _(a,V)=E₀H_(2nd)+F₀(E₀=about'5±0.5/10³,F₀=about 2.7±0.5). Work-hardening capacity of the compositemay be controlled by measuring hardness, which is one of the physicalproperties, of the phase-transformable metastable B2 second phaseprecipitated in the composite and calculate the absorbed energy (E^(p)_(a,V)) by work-hardening per unit volume fraction of the second phaseformed in the metallic glass matrix composite prepared using each of thecompositions. Particularly, since the hardness value of the second phasein the composite may be relatively measured as compared to the absorbedenergy or the martensite-start temperature, work-hardening capacity ofthe composite may be controlled by calculating the absorbed energy(E^(p) _(a,V)) by work-hardening per unit volume fraction of the secondphase formed in the metallic glass matrix composite prepared using eachof the compositions.

In short, according to the exemplary embodiment of the presentinvention, there is provided a metallic glass matrix composite withcontrollable work-hardening capacity capable of having significantlyexcellent toughness due to the metastable second phase precipitatedin-situ in the metallic glass matrix by polymorphic phase transformationduring the solidification process without a separate synthetic process,and capable of controlling work-hardening capacity by adjusting thevolume fraction of the second phase in the composite through measurementof the physical properties of the metastable B2 second phase and castingprocess control due to constant correlation between the physicalproperties (the absorbed energy E^(t) _(a), the phase transformationtemperature T_(Ms), or the hardness H_(2nd)) of the metastable B2 secondphase precipated in the metallic glass matrix in the related compositionregion and the absorbed energy (E^(p) _(a,V)) by work-hardening per unitvolume fraction of the second phase in the metallic glass matrix. Themetallic glass matrix composite may contain about 35 to 58 at % of Ti,about 35 to 50 at % of Cu, about 4.5 to 12 at % of Ni, and about 0.5 to5 at % of Si, and further contain one or more elements selected from Zr,Hf, V, Nb, Ta, Nb, and Cr, which are early transition metals (ETM), andAl and Sn, which are post transition metals (PTM), in a range of about 1to 15 at %.

Hereinabove, the exemplary embodiments of the present invention havebeen disclosed for illustrative purposes, and those skilled in the artwill appreciate that various modification are possible without departingfrom the technical spirit of the present invention. Therefore, the scopeof the present invention should analyzed by the appended claims withoutthe exemplary embodiments, and it should be analyzed that all spiritswithin a scope equivalent thereto are included in the appended claims ofthe present invention.

While this invention has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A metallic glass composite with controllablework-hardening capacity, the metallic glass composite comprising: ametallic glass matrix; and a phase-transformable metastable B2 secondphase precipitated in the metallic glass matrix by polymorphic phasetransformation wherein the work-hardening capacity is controlled byabsorbed energy (E^(t) _(a)), a phase transformation temperature(T_(Ms)), or hardness (H_(2nd)) and phase lo volume fraction (V_(f)),which are physical properties of the phase-transformable metastable B2second phase.
 2. The metallic glass composite of claim 1, wherein: themetallic glass matrix comprises about 35 at % to about 58 at % of Ti,about 35 at % to about 50 at % of Cu, about 4.5 at % to about 12 at % ofNi, and about 0.5 at % to about 5 at % of Si.
 3. The metallic glasscomposite of claim 2, wherein: the metallic glass matrix furthercomprises one or more elements selected from Zr, Hf, V, Nb, Ta, Nb, andCr, which are early transition metals (ETM), and Al and Sn, which arepost transition metals (PTM), in a range of about 1 at % to about 15 at%.
 4. The metallic glass composite of claim 1, wherein: absorbed energy(E^(p) _(a,V)) by work-hardening per unit volume fraction of aphase-transformable metastable B2 second phase in the metallic glassmatrix and absorbed energy (E^(t) _(a)) of the phase-transformablemetastable B2 seocnd phase satisfy the following Equation:E ^(p) _(a,V) =A ₀ E ^(t) _(a) −B ₀ (A₀=about 5(±0.5)/10³, B₀=about6(±3)/10²) (A₀=about 5(±0.5)/10³, B₀=about 6(±3)/10²) unit: E^(p)_(a,V)(J/cm³vol %), E^(t) _(a)(J/cm³).
 5. The metallic glass compositeof claim 1, wherein: absorbed energy (E^(p) _(a,V)) by work-hardeningper unit volume fraction of a phase-transformable metastable B2 secondphase in the metallic glass matrix and a martensite-start temperature(T_(Ms)) of the phase-transformable metasatblae B2 second phase satisfythe following Equation:E ^(p) _(a,V) =C ₀ T _(Ms) −D ₀ (C₀=about 2.6(±0.2)/10³, D₀=about1.6(±0.2)/10) unit: E^(p) _(a,V)(J/cm³vol %), T_(Ms)(K).
 6. The metallicglass composite of claim 1, wherein: absorbed energy (E^(p) _(a,V)) bywork-hardening per unit volume fraction of a phase-transformablemetastable B2 second phase in the metallic glass matrix and a hardnessvalue (H_(2nd)) of the phase-transformable metastable B2 second phasesatisfy the following Equation:E ^(p) _(a,V) =E ₀ H _(2nd) +F ₀ (E₀=about −5(±0.5)/10³, F₀=about2.7(±0.5) unit: E^(p) _(a,V)(J/cm³vol %), H_(2nd)(HV).
 7. The metallicglass composite of claim 1, wherein: a hardness value (H_(2nd)) of thephase-transformable metastable B2 second phase and a martensite-starttemeprature (T_(Ms)) thereof satisfy the following Equation:H _(2nd)=about 469.6±10'0.33±0.1T _(Ms) unit: H_(2nd)(HV), T_(Ms)(K). 8.The metallic glass composite of claim 1, wherein: controlling of avolume fraction of the phase-transformable metastable B2 second phase inthe metallic glass matrix is performed through a suction castingprocess.
 9. The metallic glass composite of claim 8, wherein: themetallic glass composite is formed by casting using arc plasma havingoutput power of about 5 V to about 50 V (output voltage) and about 30 Ato about 300 A (output current).
 10. The metallic glass composite ofclaim 8, wherein: the metallic glass composite is formed by introducinga molten metal into a mold by a pressure of about 0 torr to about 600torr and casting the molten metal.
 11. The metallic glass composite ofclaim 8, wherein: the metallic glass composite is formed by casting theinjected molten metal while adjusting cooling capacity in a range ofabout 10¹ K/s to about 10⁴ K/s.